As a technology for preventing a liquid coolant from being held up in a compressor during an operation stop of a heat pump device used in an air conditioner or the like, there has been a technology for energizing a motor winding wire without driving a motor in the compressor (hereinafter referred to as “constraint energization”) and heating the compressor to thereby vaporizing and discharging the liquid coolant. For example, Patent Literature 1 discloses a technology for, when detecting that the ambient temperature of the air conditioner is in a low-temperature state, supplying a single-phase alternating-current voltage having a frequency of about 25 kilohertz higher than a normal frequency during a normal operation to the compressor, preventing the liquid coolant from being held up in the compressor to smooth lubricating action in the compressor while suppressing an excessive temperature rise and rotation of a rotating unit of the compressor.
Further, for example, Patent Literature 2 discloses a technology for feeding a direct current to the motor winding wire according to an outdoor air temperature to thereby performing preheating of the motor without rotating a rotor making use of a copper loss generated in the motor winding wire.